1. Field of the invention
This invention relates to an alloy material for data storage and specifically to an alloy material for data storage of a magneto-optical disk and its manufacturing process. This material is characteristically based an MnBi alloy, doped with Al atoms and Si (or B) atoms. Said alloy material for data storage of a magneto optical disk in the present invention can overcome the shortcomings existing in various magneto-optical films conventionaly used at present and it satisfies the requirements with respect to a magneto-optical disk for data storage and audio, video techniques.
2. Description of Prior art
Presently, the development of computer and data storage technique needs such a material so as to be capable of storing large amounts of data which can be written in or erased again and again by lasers while the data storage function does not vary. The material of the present invention simultaneously provide the following features: i.e., it has a small signal-noise ratio (S/N) and it is not affected by temperature variation. Furthermore, its preparation process is easy and simple.
For the time being, the magneto-optical disk is widely used and several conventionally used materials for manufacturing magneto-optical disk are as follows:
(1) Amorphous crystal TbFeCo or GdTbFeCo. Such materials have advantages such as an amorphous state, i.e. the atoms are not arranged in order, no crystal grains nor noise from grain boundaries. However, the magneto-optical disk manufactured with this kind of material has a small signal-noise ratio S/N, because the S/N ratio is proportional to the magneto-optical Kerr rotation .theta. k of the material and TbFeCo or GdTbFeCo generally have a magneto-optical Kerr rotation 0.35.degree.-0.40.degree.; in addition, as this kind of material is amorphous, after being heated, its ageing is very easy, it is unstable along with temperature variation; meanwhile, as this is a rare earth material, it is subject to oxidation and expensive.
(2) yttrium iron garnet YIG film. This material is crystalline, its drawback is that the growth temperature reaches up to 600.degree. C. Hence, during its manufacture, an anti-high temperature material, such as quartz must be used as the substrate. Besides, the grain size (d) of this material generally is larger, its surface is tougher and the application effect turns out to be not very good and it needs a high power laser to write in.
(3) Superlattice film. This is a regulating film of superposed layers interstitially made of a transitional metal e.g. iron (Fe) and of a rare earth metal such as Terbium (Tb) respectively. It is also an amorphous material. As it has many layers superimposed, its interior, especially its interface has internal strain and the crystal lattice between iron/(Fe) and terbium (Tb) is mismatched; as a result, the magneto-optical disk manufactured with this material assumes unstationary, changeable performances in use and the Kerr rotation is small.
(4) Manganese bismuth (MuBi) alloy film. This is a crystalline material as well; and it has a larger magneto-optical Kerr rotation, around 0.7.degree.. But its curie point Tc is high. In addition, when the material is quenched from 375.degree. C. (near The Curie point) to room temperature corresponding to the write-in or erase process of the magneto-optical disk, its Kerr rotation will drop significantly. The grain size (d) of a manganese bismuth (Mubi) alloy material is about a few microns. Such a large grain size leads to a decrease of the read-out signal/noise ratio of the magneto-optical disk. Because of the above mentioned reasons, the practical application of this material is almost impossible.